Relay system



*May 26, 1942.l

H. E; GOLDSTINE 'RELAY SYSTEM Filed Nov. 29, 1939 Patented May 26, 1942UNITED RELAY SYSTEM Y Hallan E. Goldstne, Rocky Point, N. Y., assignerto Radio Corporation of America, a corpora--` tion of DelawareApplication November 29, 1939, Serial No. 306,608

3 Claims. ,(Cl. Z50-15) The present invention relates to the art cfsignal relaying by ultra short wave radio and, more particularly, to asystem for supplying a television signal to receivers which are near therelay system but not within the eld of the transmitters of the system.One method of utilizing a network of television relay stations toconnect important cities involves the transmission of the televisionlsignals on an ultra high frequency of the order of hundreds ofmegacycles from one city l and at intervals of fty miles, orthereabouts, picking up the received signals, amplifying andretransmitting the signals through the medium of highly directiveantennae and thus covering the entire distance between the cities. Dueto the quasi-optical characteristics of the ultra high frequencies usedthe signals are transmitted only along line of sight paths and due tothe extreme-directivity of the transmitting and receiving antenna of therelay station, as well as due to the high frequencies involved, beingbeyond the tuning range of television broadcast receivers, suchreceivers are unable to receive the programs.

An object of the present invention, therefore, is the provision of atelevision relay system which will supply a relayed television signal toa comparatively large area near the path of the television relay chain.In accordance with this object it is proposed that the television signalbe transmitted by means of frequency modulation. At the desiredlocations where low frequency broadcast transmitters are to be located apickupantenna within the field of a high frequency relay transmitter isestablished, or the signals are tapped off from an adjacent relaystation amplifier. The picked up high frequency signals are heterodynedby means of a fixed frequency oscillator to the television broadcastband and then amplified in a number of stages at that frequency untilthe power is sufficient for prnner coverage of the area involved. Thisamplified lower frequency signal is then applied to a broadcast antennain the conventional manner and radiated over the area to be covered. Asa further feature of the invention means may be provided to alter themodulation index of this broadcast signal.

Further objects and features of the invention will be more clearlyunderstood from the following detailed description which is accompaniedby a drawing in which Figure 1 shows the layout of a television relaychain and a broadcast transmitter utilizing the principles of myinvention with the amplifiers and converters shown in conventionalAblock form, and Figure 2 illustratesa modification of a portion ofFigure 1.

In Figure 1, I have shown -a plurality of they ultra high frequencyrelay stations I0, each of which are placed at the top of acomparativelytall tower. These towers are spaced about miles apart, depending uponthe characteristics of the terrain covered, and a balancing of the costper foot of the towers against the cost of the relay equipment. Each ofthe relay stations Iii comprises a receiving antenna I2 withina highlydirective reflector I3 and a similar transmitting antenna likewisewithin a highly directive transmittingreiiector I3. The receiving andtransmitting antennas are connected by an amplifier which takes thesignal as picked up by the receiving antenna, ampliiies it withoutfrequency conversion and retransmits it to the next relay in the relaystation Ill nearest the area to be covered by the broadcast signal andapplies the signal taken therefrom to a frequency converter I5. Ifdesired, the relay frequency signal may be picked up by asimple antennabetween adjacent relay stations. Since the relay transmission is afrequency modulated signal the relay transmission may have its frequencychanged to the conventional television broadcast band by means of afixed frequency oscillator such as a crystal oscillator or a frequencycontrolled oscillator of any other convenient type at I5 and amplifiedat I6 for transmission by means of transmission line I 'I to the poweramplifiers I 8. The amplified signal, of suiiicient power to cover thedesired area, is then applied to the broadcast antenna I9 in the usualmanner. Since a frequency modulated signal is used the amplifiers I6 andI8 need not be operated as linear amplifiers but need only respondlinearly with frequency, thus decreasing the cost of the systemconsiderably.

The frequency control device IEa may be either a crystal oscillator orautomatic frequency control may be applied from the output of amplifierI6, as indicated by line F-I-C, to maintain the average frequency of thesignal in transmission line Il and radiated from the antenna ISessentially constant. In some cases it may be desirable to reduce thefrequency swing or modula- A trans--v tion index of the broadcast signalfrom that existing in the relay signal. is shown inFigure 2 wherein ademodulator 26 takes a portion of the signal'frorntransmission line I4,before it is applied to the frequency converter I5. The demodulatedsignal, of an adjustable amplitude controlled by amplitude control 21One method of doing this is applied to a `frequency modulator stage 25.The frequency modulator 25 aplies the signal to Y' Vthe heterodyneoscillator in a manner to opDOSe the original frequency swing therebydegenerating. the frequency modulated signal output from converter I5 toany desired extent.

While I haveparticularly shown and described` quencies, said chainpassing .near an intermediate area overwhich signals are to bebroadcast, pick-up means adapted to Vreceive Ysaid ultra high frequencysignals connected to one ofV said vrelayv stations adjacent .said area,an oscillator,v means for applying signals picked up :by said pick-upmodulation index `of said lower frequency signals ,may be adjusted, andmeans for broadcasting v said lower frequencysignals over said area.

2. In a signal transmission system, a source of'frequency modulated highfrequency waves, a frequency rconverter inc1uding an oscillator, meansfor applying said waves to said Vfrequency `converter oscillator so thatthey are heterodyned toa different frequency, means independent of saidfrequency converter means for demodulating said first mentionedhighfrequency wavesl and means for modulating said oscillator inaccordance with saiddemodulated waves in such sense fwith respect to themodulation of said frequency modulated signals that the modulation indexof said resultant frequency modulated signals 'maybe adjusted.

rmeans to said oscillator so that said signals are heterodyned to alower frequency, means forfrequency modulating said oscillator in apredetermined sense withrespect to the modulation of said frequencymodulated signals whereby Vvthe 3. In a signal'transmission systemwherein frequency modulated waves in one frequency band "are transformedto frequency modulated waves in another frequency modulated bandfbyheterodyning in one path' :the first mentioned waves with wave energy ofa predetermined vfrevlquency, theV method of Areducing the modulationrindex ofthe secondcmentioned of said frequency Vmodulatedr waves whichcomprises 'diverting a portion ofsaid first mentioned4 wavesr into asecond path; demodulating in said' second path'said diverted portion ofsaid rst mentioned waves and frequency'modulating said wave ofpredetermined frequency by said demodulated first wave. f Y f HALLAN E.GOLDSTINE;

